Sue Epstein/The Star-LedgerThe Middlesex County courthouse is shown in this file photo. A Perth Amboy middle school teacher was convicted today of sexually assaulting a female student over a five-year period, starting when she was 13.

NEW BRUNSWICK — A Perth Amboy middle school teacher was convicted today of sexually assaulting a female student over a five-year period, starting when she was 13.

Guillermo Santamaria, also known as William Santamaria, 58, was convicted of aggravated sexual assault, two counts of sexual assault and two counts of official misconduct, including a charge that he had sex with the student on school property after she turned 18.

Middlesex County Prosecutor Bruce Kaplan said the jury deliberated two hours in New Brunswick before finding Santamaria guilty. The case was presented by assistant prosecutor Lynn Pilone.

During the five-day trial before Superior Court Judge Dennis Nieves, testimony showed that Santamaria, a social studies teacher for 16 years in Perth Amboy, sexually assaulted the girl on numerous occasions in the city from the fall of 1997 up to the victim's 18th birthday in 2002, Kaplan said.

Investigators determined the victim was a student in Perth Amboy at the times of the offenses.

The investigation began after the victim contacted the county prosecutor's office in April 2010.

Following the conviction, Superior Court Judge Dennis Nieves revoked the teacher's $250,000 bail and he was taken to the Middlesex County jail.

Santamaria will be sentenced Sept. 28 and faces up to 30 years in prison.